tests\haddock-options from GHC 9.6.6 to GHC 9.8.4: changed behaviour, why?

[mpilgrem]

Moving from GHC 9.6.6 (LTS 22.43, Cabal-3.10.3.0 and haddock --version 2.29.2) to GHC 9.8.4 (LTS 23.0, Cabal-3.10.3.0 and haddock --version 2.30.0) the integration test haddock-options changed its behaviour, in that haddock -haddock-arguments --optghc=-DBAR failed to fail.

With tests\integration\tests\haddock-options\files as the working directory and LTS 22.43 (extracts, reformatted):

❯ stack --snapshot lts-22.43 haddock --haddock-arguments --optghc=-DBAR
haddock-options> configure (lib)
...
haddock-options> haddock
Preprocessing library for haddock-options-0.1.0.0..
Running Haddock on library for haddock-options-0.1.0.0..
Warning: The documentation for the following packages are not installed. No
links will be generated to these packages: base-4.18.2.1, ghc-bignum-1.3,
ghc-prim-0.10.0

src\Lib.hs:10:2: error:  error: FOO and BAR is defined
   |
10 | #error FOO and BAR is defined
   |  ^
#error FOO and BAR is defined
 ^
1 error generated.

src\Lib.hs:1:1: error:
    `clang.exe' failed in phase `C pre-processor'. (Exit code: 1)
  |
1 | {-# LANGUAGE CPP #-}
  | ^

Error: [S-7282]
       Stack failed to execute the build plan.

       While executing the build plan, Stack encountered the error:

       [S-7011]
       While building package haddock-options-0.1.0.0 (scroll up to its section to see the error) using:
       D:\sr\setup-exe-cache\x86_64-windows\Cabal-simple_O_vy6YIf_3.10.3.0_ghc-9.6.6.exe 
       --verbose=1 
       --builddir=.stack-work\dist\effaccc7 
       haddock 
       --html 
       --hoogle 
       --html-location=../$pkg-$version/ 
       --haddock-option=--hyperlinked-source 
       --haddock-option=--quickjump 
       --haddock-option=--optghc=-DBAR 
       --haddock-option=--optghc=-DFOO
       Process exited with code: ExitFailure 1

and (LTS 23.0) (extracts):

❯ stack haddock --haddock-arguments --optghc=-DBAR
haddock-options> configure (lib)
...
haddock-options> haddock
Preprocessing library for haddock-options-0.1.0.0..
Warning: The documentation for the following packages are not installed. No
Running Haddock on library for haddock-options-0.1.0.0..
links will be generated to these packages: base-4.19.2.0, ghc-bignum-1.3,
ghc-prim-0.11.0

src\Lib.hs:10:2: error:  error: FOO and BAR is defined
   |
10 | #error FOO and BAR is defined
   |  ^
#error FOO and BAR is defined
 ^
1 error generated.
Haddock coverage:
haddock: Unable to find a package providing module <no-mod>, skipping Hoogle.

         Perhaps try specifying the desired package explicitly using the --package-name
         and --package-version arguments.

Documentation created: .stack-work\dist\f24b2e15\doc\html\haddock-options\,
.stack-work\dist\f24b2e15\doc\html\haddock-options\haddock-options.txt
haddock-options> copy/register
Installing library in ...\.stack-work\install\854890af\lib\x86_64-windows-ghc-9.8.4\haddock-options-0.1.0.0-CuGz8FXsCXtFtA73xMP0Gw
Registering library for haddock-options-0.1.0.0..
Updating Haddock index for project packages in:
...\.stack-work\install\854890af\doc\index.html
Updating Haddock index for project packages and dependencies in:
...\.stack-work\install\854890af\doc\all\index.html

where, before copy/register (using --verbose):

Process finished in 6572ms: D:\sr\setup-exe-cache\x86_64-windows\Cabal-simple_O_vy6YIf_3.10.3.0_ghc-9.8.4.exe 
--verbose=1 
--builddir=.stack-work\dist\f24b2e15 
haddock 
--html 
--hoogle 
--html-location=../$pkg-$version/ 
--haddock-option=--hyperlinked-source 
--haddock-option=--quickjump 
--haddock-option=--optghc=-DBAR 
--haddock-option=--optghc=-DFOO

The haddock command is unchanged, so it seems likely a change in the behaviour of the haddock executable.